* It acquires two phases shifts depending on the evolution. The dynamical phase, $\theta_n(t)$, and the geometrical phase $\gamma_n(t)$. They are given as,
* It acquires two phases shifts depending on the evolution. The dynamical phase, $\theta_n(t)$, and the geometrical phase $\gamma_n(t)$. They are given as,
In order for this description to hold, we require that the system evolves slowly enough. That is, the following condition must be satisfied at all times:
In order for this description to hold, we require that the system evolves slowly enough. That is, the following condition must be satisfied at all times:
$$
$$
\frac{\hbar \overline{\langle \psi_n | \dot H |\psi_m\rangle} }{\overline{E_n - E_m}^2} << 1, \quad n \neq m.
\frac{\hbar \overline{\langle \psi_n | \dot H |\psi_m\rangle} }{\overline{E_n - E_m}^2} << 1, \quad n \neq m.
$$
$$
Here, the overline indicates the largest matrix element, and the smallest energy difference.
Here, the overline indicates the largest matrix element, and the smallest energy difference.